1. Field of the Invention
The present invention relates to an improved rolling apparatus for forming part of a steel plate into a thin walled portion.
2. Description of the Related Art
As a method for forming part of a steel plate into a thin walled portion, there are generally known a method comprising the step of welding together a plurality of plates of different thickness and a method employing rolling.
FIG. 15A and FIG. 15B hereof illustrate a method for forming part of a steel plate into a thin walled portion by welding.
In FIG. 15A, a differential thickness steel plate 120 having a thin walled portion is shown which is produced by superposing one side end portions of thick plate materials 122, 123 by respective widths t1 and t2 on respective side end portions of a thin plate material 121 and spot welding the thin plate material 121 and thick plate materials 122, 123 together.
In FIG. 15B, a similar differential thickness steel plate is shown which is produced by superposing thick plate materials 122 and 123 on a thin plate material 121 and laser welding the same together. The thick plate materials 122 and 123 have respective angles xcex2 and xcex8 on respective end faces thereof. The formation of the angles xcex2 and xcex8 is intended to decrease excessive thick plate materials to contrive weight saving of the objective plate.
However, the spot welding as illustrated in FIG. 15A involves such problems as increases in the number of parts and processing steps and lowering of rigidity. In addition, superposing widths t1 and t2 of the thin plate material 121 result in an increase in the overall weight of the differential thickness plate materials 120 by the weight of the superposed portion.
On the other hand, the laser welding as illustrated in FIG. 15B involves such problems as accuracy and precision required in the grooves of the two different plate materials, an increase in the welding apparatus cost and deterioration in the shaping property of welding portions.
To this end, an apparatus for producing a differential thickness plate without the use of welding has been proposed, for example, in Japanese Patent Laid-Open Publication No. SHO-59-189004 entitled xe2x80x9cMETHOD FOR PRODUCING DIFFERENTIAL THICKNESS PLATE AND ROLLING MILL THEREFORxe2x80x9d. The rolling mill for the production of a differential thickness plate produces such a plate by enabling an upside working roll and an underside working roll to be driven and controlled independently of each other, driving the underside working roll in a direction reverse to the driving direction of the upside working roll, and thus roll forming a plate.
However, since in the rolling mill disclosed therein, the upside working roll and underside working roll are driven and controlled independently of each other, control in general such as control for rolling load, rolling speed, plate thickness and the like becomes complicated and this leads to increases in the installation cost, thus increasing the production cost of the differential thickness plate.
The present invention has been attained to overcome the foregoing problems. It is accordingly an object of the present invention to provide a rolling apparatus capable of producing a differential plate thickness without the use of advanced technique.
According to an aspect of the present invention, there is provided a rolling apparatus comprising: a plurality of clamping means for grasping a steel strip, the clamping means being separated in a direction of transfer of the steel strip; tension imparting means for moving at least one of the clamping means in a tension direction to apply a predetermined tension to the steel strip grasped by the clamping means; a traveling table for reciprocally moving the clamping means and the tension imparting means in unison longitudinally of the steel strip; and a rolling means for pressing down with upper and lower rolling rolls the steel strip grasped by the clamping means placed on the traveling table.
In the above-mentioned rolling apparatus, the steel strip is grasped by the clamping means spaced in a direction of conveyance of the strip. The clamping means are moved by the tension imparting means. While a tension is applied to the steel strip, a thin walled portion is formed on part of the steel strip. The tension, when applied to the thin walled portion, facilitates formation of the thin walled portion with a rolling roll. As a result, a high degree of control is not needed for the rolling means. In addition, by reciprocally moving the strip in a conveying direction, a thin walled portion is formed on part of the steel strip.
In a preferred form. the rolling apparatus is further equipped with a turntable to rotatably support the rolling means. By operating the turntable, the axes of the upper and lower rolling rolls are set non-perpendicularly to the longitudinal direction of the steel strip, thereby enabling the thin walled portion to be formed in a trapezoidal form. Likewise, it is made possible to form the borderline between the thin walled portion and the thick walled portion at a desirable angle and also constitute only a portion requiring strength of the thick walled portion.
It is preferable to provide a heating means for heating the steel strip on both the upstream side and the downstream side of at least either of the upper and lower rolling means, since rolling work of the steel strip is facilitated by heating with the heating means, and the rolling time can be shortened.